Rotary kiln for the recovery of acid values



March 4, 1952 H, MILEY ROTARY KILN FOR THE RECOVERY 0F ACID VALUES Filed Aug. 12. 1947 1N V EN TOR. 17u/nier /Wzly v@ ,l

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Patented Mar. 4, 1952 ROTARY KILN FOR THE RECOVERY 0F ACID VALUES Hunter Miley, Petrolia, Pa., assignor to L. Sonneborn Sons, Inc., a corporation of Delaware Application August 12, 1947, Serial No. 768,112 s claims. (ci. 23-279) sludges are produced in the oil industry and the recovery of sulfuric acid values therefrompresents a major problem.

Petroleum relining sulfuric acid sludges when heated to temperatures in excess of 500 F. are substantially decomposed into gaseous decomposition products comprising SO2, water and oil vapors and a carbonaceous residual material `usually referred to as coke. Various methods have i been proposed in the past for the recovery of acid values from these and similar sludges utilizing -this thermal decomposition. One such method involves the use of rotary kilns and decomposition of the sludge by direct contact with hot combust-ion gases usually in a counter-'current arrangement Within the kiln. The decomposing sludge passes through three main decomposition phases, i. e., liquid, semi-liquid and finally solid residual coke. In'going through the semi-liquid stage, large balls of gummy material like bigmasses of dough are formed which must be broken up, kneaded and mixed to keep the kiln from being clogged and to assure satisfactory decomposition. This is usually accomplishedY by steel rods or bars that are lifted and dropped on the material within the kiln as the same revolves. Frequent renewals of the kiln bars or rods due to the corrosive action of the sludge is necessary. Furthermore, the pounding resulting from the action of these rods or bars necessitates the frequent repair and renewal of the kiln linings. Still further the use of the hot decomposition gases in the l'thermal decomposition of the sludge entails a considerable dilution of the SO2 gas Amixture issuing from the kiln. For the latter reason the application of the rotary kiln method is limited to the processing of acid sludges 10W in oil content since a high oil content produces a relatively large volume of combustion gases which render the SO2 bearing vapors too dilute for economical conversion to H2804.

One object of the invention comprises inter alla an improvement in rotary kilns of the l.hitherto used types in which the disadvantages 2 -of th-e pounding action of rods or bars as hitherto used, is substantially eliminated.

Another object of the invention comprises an improvement in rotary kilns in which the thermal decomposition is carried out substantially avoiding undesirable dilution of SO2-bearing decomposition gases from the kiln.

The foregoing and still further objects of the invention will be more fully understood from the following description read in conjunction with the accompanying drawing representing a side View of a preferred embodiment of the invention with parts cut away and parts in cross-section.

A rotary kiln shell l is substantially horizontally disposed and is provided with outer guide rings 2 and 3 and centrally located gear toothed guide ring 4. Guide rings 2 and 3 are slidably engaged by U-shaped guides 5 and 6 respectively, each being supported by way of guide supports S and blocks@ resting on concrete foundation block Ill. The toothed central guide ring 4 is engaged by the gear il driven by shaft I2 through pulley I3 by a motor (not shown). Shaft l2 rests in bearings it secured to blocks l5 which rest on the central foundation block i6. A substantially stationary gas hood Il' is mounted at one end of the rotary kiln shell 'l and is provided with a gas take-off i8. Acid sludge feed I9 passes through gas hood il into the interior of kiln shell l. Friction rings 2D and 2| are secured to the gas hood il and the ange 22 of shell l to establish therebetween the friction joint 23.

A coke discharge hood 29 is provided at the end of the kiln away from the sludge feed i9. Flange member 3G carried by the exterior of the kiln shell I is secured to friction ring 3i. A friction ring 32 is carried by the coke discharge hood 29 and the friction rings 3l and 32 establish therebetween a friction fit 33. The coke discharge hood 29 is also mounted substantially stationary.

A roller 3d provided with a helix 35 is loosely positioned Within the rotary kiln shell l to rest with the helix on the inner surface thereof. A closure plate 2li is provided at the gas hood end of the kiln carrying rods 25 secured to springs 25 resting against the interior or gas hood l'l guided by Way of the bolts2'l. Closure plate 24 provides at 28 a friction closure, for the interior of roller 34. vHeating gas outlet 36 extends through gas take-off hood I1 and closure 24 into the interior of thevhelicoid roller 34. A substantially station- Aary friction closure 31 is provided at the coke discharge end of the kiln. friction surface 38 with the roller 35. Rods 39 It defines closure secured to springs 'l passing to coke discharge hood 29 carrying the spring guide rods lli press friction closure 3l against its end of the helicoid roller 3. A heating gas inlet l2 suitablyr supportedon, for instance, concrete block 43 extends through coke discharge hood 29 and closure 3l l2, gear l l and toothed guide ring G. Acid sludge 1:

is passed through the feed pipe I9 into the interior ofthe rotating kiln shell i. A suitable heating medium, such as hot air combustion gases or the like, is passed through the heating gas inlet 42 into the interior of the helicoid roller 34 and out through the heating gas outlet 36. Through heat exchange Within the helicoid roller the same heats up and transmits its heat to the acid sludge, thermally decomposing the same. The thermal decomposition of the acid sludge progresses gradually and as the rotary kiln shell l rotates, for instance, in a clockwise direction (viewed from the coke discharge end) the friction between the helix 35 and the rotating inner surface of shell l and/or sludge material in various stages of decomposition will cause the helicoid roller to rotate in the same direction. The helixthen acts essentially to feed sludge material and/or decomposed sludge material forward towards the coke discharge end. At the. same time it has a kneading and mixing effect and a breaking up eect upon any large masses of more-or-less solid decomposition materials formed or 1baked onto the shell. Thus as the heating gases move from the coke discharge to the gas take-off, the sludge material Y:

passes from the gas take-olf end to the coke discharge end, being in this counter-current arrangement gradually more and more decomposed as it is progressively moved forward by the helix on the helicoid roller.

Though the helicoid roller 34 is substantially loosely positioned within the shell I, it is substantially confined in longitudinal or axial movement by the closures 245 and 3l respectively. The springs 25 and Ml hold the closures in frictional engagement position with the roller ends, thus essentially serving as spacing means for each end of the helicoid roller as well as permitting longitudinal roller expansion caused by the heat. The

continuously broken up solid decomposition prodo ucts are finally discharged into the coke discharge hood 29 and are taken off through the outlet 4d. The SO2-bearing decomposition gases pass out through the gas hood il and the gas take-off I8. Though the frictional fits at 28 and 'f 38 between the closures at the respective ends of the helicoid roller `will in most cases suffice to prevent undue leakage of heating medium, such as combustion gases from the interior of the helicoid roller into the interior of the rotary kiln fshell l, or the leakage of SO2-bearing decomposition gases from the interior of the kiln shell i into the interior of the helicoid roller 34, I find it advisable to provide suitable to maintain a balanced vacuum lwithin the syst m. Thus, for instance, an automatically controlled valve such as the butterfly valve d5 in heating gas outlet 35 and the butterfly valve 46 in gas take-of.F i8, may be provided. It is then possible to maintain a suitable pressure diiferential as between the interior of the helicoid roller 3i and the portion 36-a of the outlet 35 on the one hand and between the interior of rotary shell i and the portion I8-a of gas take-off i3. Thus, if for instance the pressure in part 36-c is less than that obtaining in the interior of shell l, the preferential gas flow will be through the outlet 36 with a minimum of leakage at 28 and 38. If then the pressure in gas take-olf portion lil-a is lower than the pressure inside the helicoid roller 34, the preferential discharge of decomposition gases will be through the gas take-olf i8 and practically no leakage into the interior of helicoid roller 3i will occur at the friction joints 28 and 38.

'Within the preferred embodiment of my invention I find it of advantage to provide the interior of the .helicoid roller with suitable means to facilitate the heat exchange between the heating medium and the walls of the helicoid roller 3. Thus, for instance, suitable heat exchange fins 41 may be provided. In the drawings, for the find it of advantage to arrange the same on the interior walls of the helicoid roller 3 substantially in the nature of a screw or thread angled in a direction substantially opposite to that of the helix.

Broadly speaking, the invention essentially emraces in a rotary kiln of the horizont-ally disposed type for the recovery of acid values from sulfuric acid sludges and having a rotatable kiln shell, a gas take-off from and sludge feed into said shell, the improvement which comprises a roller substantially loosely positioned Within said shell, and a helix provided on the cricumference of said roller, said roller resting with said helix on the inner surface of said shell and being substantially conned against appreciable longitudinal movement, the decomposition kiln so described is used in a method for recovery of acid values set forth in my copending application Serial No. 768,113, filed August 12, 1947.

When using theimprovement in accordance with the invention the SO2-bearing decomposition gases issuing from the gas take-off i8 are subjected in accordance with conventional practice to a water condensation step which will effectively remove therefrom substantially all condensable matter such as water and vapcrized hydrocarbon material. The gas issuing from the condensation is substantially free from undesirable combustion gas diluents and contains a high concentration, sometimes as high as 98% SO2.

The foregoing description is for purposes of illustration and not of limitation and it is therefore my intention that the invention be limited only by the appended claim or their equivalents wherein I have endeavored to claim broadly all inherent novelty.

I claim:

1. In a rotary kiln of the horizontally disposed type for the recovery of acid values from sulfuric acid sludges and having a rotatable kiln shell, a gas take-off from and sludge feed into said shell, the improvement which comprises a substantially hollow roller substantially loosely positioned within said shell, a helix provided on the circumference of said roller, said roller resting with said helix on the inner surface of said shell and being Til 3. 'Improvement according to claim 1 in whichv 5 the heating gas inlet is at the coke discharge end of the kiln and the heating gas outlet is at the sludge feed end.

4. Improvement according to claim 3 in which the interior of said roller is provided with heat exchange iins.

5. In a rotary kiln of the horizontally disposed type for the recovery of acid values from sulfuric acid sludges and having a rotatable kiln shell, a gas take-off from and sludge feed into said shell, the improvement which comprises a substantially hollow roller substantially loosely positioned within said shell, a helix provided on the circumference of said roller, said roller resting with said helix on the inner surface of said shell, a friction closure at each end of said roller and each held against its roller end by springv force, a heating gas inlet through one of said closures into said roller at the roller end removed from said sludge feed, and a heating gas outlet through the other said closure out of said roller. g

6. Improvement according to claim 5 in which the interior of said roller is provided with heat exchange ilns.

7. Improvement according to claim 5 in which there are additionally provided means in said gas take-01T and in said heating gas outlet for substantially maintaining a balanced vacuum in each to substantially avoid gas leakage between the interior of said shell and the interior of said roller.

8. Improvement according to claim 'I in which the interior of said roller is provided with heat exchange ns extending in screw fashion angled in a direction substantially opposite to that of said helix.

HUNTER MILEY.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS 

1. IN A ROTARY KILN OF THE HORIZONTALLY DISPOSED TYPE FOR THE RECOVERY OF ACID VALUES FROM SULFURIC ACID SLUDGES AND HAVING A ROTATABLE KILN SHELL, A GAS TAKE-OFF FROM AND SLUDGE FEED INTO SAID SHELL, THE IMPROVEMENT WHICH COMPRISES A SUBSTANTIALLY HOLLOW ROLLER SUBSTANTIALLY LOOSELY POSITIONED WITHIN SAID SHELL, A HELIX PROVIDED ON THE CIRCUMFERENCE OF SAID ROLLER, SAID ROLLER RESTING WITH SAID HELIX ON THE INNER SURFACE OF SAID SHELL AND BEING SUBSTANTIALLY CONFINED AGAINST APPRECIABLE LONGITUDINAL MOVEMENT AND THE INTERIOR OF SAID ROLLER BEING SUBSTANTIALLY CLOSED AGAINST THE INTERIOR OF 